/*
* Copyright 2010-2017 JetBrains s.r.o.
*
* Licensed under the Apache License, Version 2.0 (the "License");
* you may not use this file except in compliance with the License.
* You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*/
package org.jetbrains.kotlin.contracts.model.visitors
import org.jetbrains.kotlin.contracts.model.*
import org.jetbrains.kotlin.contracts.model.structure.*
import org.jetbrains.kotlin.types.typeUtil.isSubtypeOf
/**
* Reduces given list of effects by evaluating constant expressions,
* throwing away senseless checks and infeasible clauses, etc.
*/
class Reducer : ESExpressionVisitor<ESExpression?> {
fun reduceEffects(schema: List<ESEffect>): List<ESEffect> =
schema.mapNotNull { reduceEffect(it) }
private fun reduceEffect(effect: ESEffect): ESEffect? {
when (effect) {
is SimpleEffect -> return effect
is ConditionalEffect -> {
// Reduce condition
val reducedCondition = effect.condition.accept(this) ?: return null
// Filter never executed conditions
if (reducedCondition is ESConstant && reducedCondition == ESConstant.FALSE) return null
// Add always firing effects
if (reducedCondition is ESConstant && reducedCondition == ESConstant.TRUE) return effect.simpleEffect
// Leave everything else as is
return effect
}
}
}
override fun visitIs(isOperator: ESIs): ESExpression {
val reducedArg = isOperator.left.accept(this) as ESValue
val result = when (reducedArg) {
is ESConstant -> reducedArg.type.isSubtypeOf(isOperator.functor.type)
is ESVariable -> if (reducedArg.type?.isSubtypeOf(isOperator.functor.type) == true) true else null
else -> throw IllegalStateException("Unknown ESValue: $reducedArg")
}
// Result is unknown, do not evaluate
result ?: return ESIs(reducedArg, isOperator.functor)
return result.xor(isOperator.functor.isNegated).lift()
}
override fun visitEqual(equal: ESEqual): ESExpression {
val reducedLeft = equal.left.accept(this) as ESValue
val reducedRight = equal.right
if (reducedLeft is ESConstant) return (reducedLeft == reducedRight).xor(equal.functor.isNegated).lift()
return ESEqual(reducedLeft, reducedRight, equal.functor.isNegated)
}
override fun visitAnd(and: ESAnd): ESExpression? {
val reducedLeft = and.left.accept(this) ?: return null
val reducedRight = and.right.accept(this) ?: return null
return when {
reducedLeft == false.lift() || reducedRight == false.lift() -> false.lift()
reducedLeft == true.lift() -> reducedRight
reducedRight == true.lift() -> reducedLeft
else -> ESAnd(reducedLeft, reducedRight)
}
}
override fun visitOr(or: ESOr): ESExpression? {
val reducedLeft = or.left.accept(this) ?: return null
val reducedRight = or.right.accept(this) ?: return null
return when {
reducedLeft == true.lift() || reducedRight == true.lift() -> true.lift()
reducedLeft == false.lift() -> reducedRight
reducedRight == false.lift() -> reducedLeft
else -> ESOr(reducedLeft, reducedRight)
}
}
override fun visitNot(not: ESNot): ESExpression? {
val reducedArg = not.arg.accept(this) ?: return null
return when (reducedArg) {
ESConstant.TRUE -> ESConstant.FALSE
ESConstant.FALSE -> ESConstant.TRUE
else -> reducedArg
}
}
override fun visitVariable(esVariable: ESVariable): ESVariable = esVariable
override fun visitConstant(esConstant: ESConstant): ESConstant = esConstant
}